1. Field of Invention
The present invention relates generally to a cellular phone and specifically to a power management unit for the cellular phone.
2. Related Art
Cellular phones have evolved from large devices that were only capable of analog voice communications to comparatively smaller devices that are capable of digital voice communications and digital data communications, such as Short Message Service (SMS) for text messaging, email, packet switching for access to the Internet, gaming, Bluetooth, and Multimedia Messaging Service (MMS) to provide some examples. In addition to these capabilities, the cellular phones of today have additional non-communication related capabilities, such as a camera with video recording, an MPEG-1 Audio Layer 3 (MP3) player, and software applications such as a calendar and a phone book, to provide some examples. Even in light of these capabilities, manufacturers of cellular phones are placing even more capabilities into cellular phones and making these more powerful cellular phones smaller.
At the heart of each cellular phone lies a power management unit (PMU). The PMU is responsible for monitoring power connections and battery charges, charging batteries when necessary, and controlling power to other integrated circuits, as well as other power functions of the cellular phone. For example, the PMU may provide power to other integrated circuits of the cellular phone such as a radio frequency (RF) transceiver. The RF transceiver uses a portion of the frequency spectrum that is allocated to the cellular phone, commonly referred to as a communication channel, to provide bi-directional communication between the cellular phone and a cellular network. The PMU is often clocked using a frequency whose harmonics fall within the communication channel currently being used by the RF transceiver. In doing so, the PMU couples noise onto this communication channel.
Global System for Mobile Communications (GSM) is a global cellular network communication standard that defines boundaries in noise that a cellular phone may transmit onto the cellular network. The noise coupled onto the communication channel by the PMU may cause the cellular phone to exceed these boundaries. As a result, the cellular phone may be prohibited from communicating on the cellular network.
Thus, there is a need to adjust the operating frequency of the PMU so that the harmonics of the operating frequency do not fall within the frequency channel being used by the RF transceiver. Further aspects and advantages of the present invention will become apparent from the detailed description that follows.
The invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.